Aspects of the invention relate to a pile driver system for installing or removing (decommissioning) foundation elements, such as piles, anchors, and conductors, in a subsea ground formation, comprising a closed housing defining a cavity, an impact weight accommodated inside the housing, i.e. in the cavity and enveloped by the housing, and a hydraulic circuit for reciprocating the impact weight. The circuit comprises one or more valves, a cylinder, and a piston accommodated in the cylinder and connected to the impact weight, e.g. forming an integral whole with the impact weight or rigidly connected to the impact weight. The system further comprises a pump for withdrawing water from the surroundings of the pile driver and providing pressurized water to the hydraulic circuit. An aspect of the invention further relates to a method of installing or removing foundation elements.